BRYOZOA. 327 



forms. The value of a character must be determined by its 

 constancy and degree of prevalence, and experience will show 

 that the value is not by any means the same when observed 

 in different groups of species. Thus a character may be suffi- 

 ciently constant in one set of forms to be considered of generic 

 importance, while in other species the same peculiarity may be 

 found so variable that its value is almost over estimated, when 

 we call it specific. As an instance of this variability in the 

 significance of a character I may mention the two "mesopores" 

 whir-h are constantly present between the ends of the cells of 

 Ph&nopora, Hall. In other respects this genus is almost identi- 

 cal with Ptilodictva Lonsdale. In this case, therefore, the 

 position and number of the "mesopores" is a generic character. 

 In Stictoporella and Intrapora Hall, precisely the same kind of 

 "mesopores" are constantly present, but as they vary in num- 

 ber and position (even in the same species) their arrangement 

 in these cases is only of specific value. 



This naturally suggests the question, when are we justified in 

 considering a variation as having generic, specific or only 

 varietal importance? In the first place, the answer depends 

 very much upon the views held by the individual who is to 

 make the divisions. Some authors make genera and species 

 upon a very small margin, while others give their divisions un- 

 due latitude. My own plan is simple enough, and so far as I 

 can see, fills all the requirements of classification, as the result 

 is a system that is convenient as well as natural. Convenience 

 is a necessity, and, in the framing of a classification, must be 

 taken into consideration just as much as the natural relations 

 of the organisms we seek to arrange. These two necessary fea- 

 tures of a permanent classification I have sought to furnish in 

 the system here proposed. With what success will be determined 

 by future research. That it will be lacking in many points of 

 minor detail I do not doubt, yet, taken as a whole, I feel con- 

 vinced that it will meet with favor. Some of the older palaeon- 

 tologists will doubtlessly object to what they consider my ex- 

 cessive multiplication of species and genera. The same com- 

 plaint will come from other naturalists who are endowed with 

 more than ordinary ability in solving genealogical problems. 

 The first class of dissenters belong to the old school of natur- 

 alists, the second are extremists of the new. Opposed to these 



